The following patents and/or commonly assigned patent applications are hereby incorporated herein by reference:
1. Field of the Invention
This invention relates to the field of display systems, more particularly to scrolling color recapture projection display systems.
2. Background of the Invention
Viewers evaluate display systems based on many criteria such as image size, resolution, contrast ratio, color purity, and brightness. Image brightness is a particularly important metric in many display markets since the available brightness can limit the image size of a projected image and controls how well the image can be seen in venues having high levels of ambient light.
Projection display designers increase the brightness of a given projection display by increasing the light source used to form the image. Increasing the light source, however, also increases the cost, size, and weight of the display system. Additionally, larger light sources generate additional heat that must be dissipated by the display.
Many other factors affect the brightness of the images produced by the display system. One of the major factors is the number of modulators used to modulate the light used to produce the image. Display systems that use a modulator with a very fast response time, such as the Digital Micromirror Device(trademark), can use a single modulator to create a full color image. Other display systems use three modulators, such as liquid crystal display (LCD) panels or micromirrors, to create a full color image.
Micromirror-based display systems typically operate the micromirrors in a digital, or bistable, manner. Digital operation fully deflects a given micromirror to either a first position or a second position. The illumination optics of the display device illuminate the entire array of micromirror cells. Micromirrors deflected to the first position reflect light along a first path, whereas micromirrors deflected to a second position reflect light along a second path. The projection optics of the display system collects the light from the mirrors in the first position and focus the light onto an image plane. The light reflected by mirrors in the second position is prevented from reaching the image plane. An image pixel associated with a mirror in the first position is brightly illuminated, whereas an image pixel associated with mirrors in the second position are not illuminated.
Pulse width modulation creates the perception of gray scale intensities with a digital micromirror device or other spatial light modulator. When using pulse width modulation, a given micromirror element is rapidly turned on and off in response to a digital intensity word. The duty cycle of the mirror determines the total amount of light contributed to an image pixel. If the pixel is pulsed quickly enough, the human eye will accurately measure the average intensity of the pixel, but will fail to detect the pulsing.
Full-color images also are produced by taking advantage of the relatively slow response time of the human eye. Each frame period is divided into at least three periods. During each period, a primary color image is produced. If the primary color images are produced in rapid succession, the eye will perceive a single full-color-image.
An alternative to the sequential color display system is a three-modulator display system. The three-modulator display system is very similar to the sequential color display system in that they both form full color images by the combining three primary color images. The disadvantage of the three-modulator display system is the cost of the three modulators and the complex optics required both to split the white light beam from the light source into three primary color light beams and to recombine the modulated primary color light beams.
The disadvantage of the single-modulator sequential color display systems is its low image brightness. Because the white light source is time-divided into three primary color light beams, most of the light at any given time is not used. For example, when the blue primary color image is being formed, the green and red output of the white light source are filtered out of the light beam. Thus, a sequential color display system, while generally less expensive than the three-modulator display system, makes very inefficient use of the light produced by the light source.
The lost light not only reduces the brightness of the image produced by the display system, discarding the light creates several problems for the display system. The light filtered out of the light beam generally becomes stray light that the display system must control to prevent from reaching the image plane and degrading the contrast of the displayed image. The off-primary light is generally converted to heat. The heat must be dissipated by using larger fans, which in turn increase the noise produced by the display system and increase the size of the display system.
A recently developed projector architecture, commonly called sequential color recapture or scrolling color recycling (SCR), uses a sequential color filter with filter segments small enough that at least one of each primary color, and white if used, are simultaneously imaged on the modulator. The light rejected by the filter is reflected and presented to the filter a second time, hopefully to another filter segment. Assuming the recycling mechanism is perfectly efficient, the system has the effect of directing all of the light of each primary color to the corresponding primary color filter and is therefore potentially as bright as a three modulator system. Considering the inefficiencies involved the system is 1.5 to 1.8 times as bright as a comparable one modulator system.
The SCR illumination system is difficult to use with conventional micromirror devices. Conventional micromirror devices group many rows together in a reset group and apply the same reset bias voltage to the entire group. Since many entire rows must be reset simultaneously, it is difficult to track the shadow of the filter boundary across the face of the modulator. What is needed is a system and method to allow efficient use of an SCR illumination system with a block reset device such as a micromirror.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for efficient scrolling color recycling with a line-addressed modulator. One embodiment of the claimed invention provides a display system. The display system comprising: a light source, a recycling integrator rod, a sequential color filter a spatial light modulator, distortion optics, and a controller. The light source produces producing a beam of white light along a path. The sequential color filter receives the beam of white light to form a filtered beam of light having a first cross section. The spatial light modulator has a second cross section. The distortion optics on an optical path between the sequential color filter and the spatial light modulator. The distortion optics operable to receive and distort the filtered beam of light to form a filtered beam of light having a second cross section. The controller is electrically connected to the spatial light modulator for providing image data to the spatial light modulator. The spatial light modulator being operable to modulate the filtered beam according to the image data.
Another embodiment of the claimed invention provides a display system. The display system comprising: a light source, a sequential color filter a spatial light modulator, distortion optics, and a controller. The light source produces producing a beam of white light along a path. The sequential color filter comprising a spiral color wheel. The sequential color filter receives the beam of white light to form a filtered beam of light having a first cross section. The first cross section having at least one curved side following a boundary between two segments on the spiral color wheel. The spatial light modulator has a second cross section. The distortion optics on an optical path between the sequential color filter and the spatial light modulator. The distortion optics operable to receive and distort the filtered beam of light to form a filtered beam of light having a second cross section. The controller is electrically connected to the spatial light modulator for providing image data to the spatial light modulator. The spatial light modulator being operable to modulate the filtered beam according to the image data.
Another embodiment of the present invention provides a method of illuminating a spatial light modulator. The method comprising: producing a beam of white light along a path; sequentially color filtering the beam of white light to form a filtered beam of light having a first cross section; distorting the filtered beam of light to have a second cross section; and spatially modulating the distorted beam of light using a spatial light modulator, the distorting operable to improve the alignment of filter boundaries to groups of spatial light modular elements.
Another embodiment of the present invention provides a method of illuminating a spatial light modulator. The method comprising: producing a beam of white light along a path; sequentially color filtering the beam of white light using a spiral color wheel to form a filtered beam of light having a first cross section, the first cross section having at least one curved side following a boundary between two segments on the spiral color wheel; recycling light rejected by the color filtering using a recycling integrator on the path of the white light beam, the recycling integrator having an exit aperture defining the first cross section; distorting the filtered beam of light to have a second cross section; and spatially modulating the distorted beam of light using a spatial light modulator, the distorting operable to improve the alignment of filter boundaries to groups of spatial light modular elements.